How can I add more god rays coming out of the holes?
Instead of adding mist to the whole scene you can cheat and just put the rays over your text. 





I just extruded the text in z space and gave it a volume scatter and absorbtion material. All you need to do is change the density to have it look stronger. 

hope this could work for you. 

EDIT : 

The problem is with your SVG file. 



The "&amp;" symbol and the other complicated part to the logo should only have the outline. You don't need all those lines inside the "&amp;" symbol. So I would clean up the SVG file (edit>select all the vertices you dont need> delete). Make it as clean as possible. Also you need the inverse of SVG file. I would bring it back into Illustrator (or whatever you use) and Inverse the colors. You need the lettering to be extruding not the outline. 

Here is a pic where you can tell the clean parts from the weird parts. 


If possible go back to illustrator clean up the logo so it is more basic (just for the god rays). When you import it into Blender make sure after you scale it up so you can see it, that you go to OBJECT>APPLY>SCALE. And only after that go to the curves tab and go to the extrusion setting and I put in .10, but adjust to your liking.